Wondering whether there may be something contractual?
If an operator / rolling stock company decides to defer commissioing and related remediation activities, until after a period of storage, it seems reasonable that the operator / rolling stock company (rather than the manufacturer) should be liable for any additional costs arising. Otherwise the manufacturer would be liable for the costs of retaining a team to support commissioining and perform any resulting remediation, and also for maintaining related commissioning / remediation facilities, for longer than would otherwise have been necessary, had the trains been commissioned immediately following handover.
And so there may be a clause in the contract along the lines of the manufacturer, not being liable for remediation costs arising from commissioning activities beyond a fixed period after handover to operator / roling stock company (for commmissioning).
Is this a thing?
Conjecture.
But it could be.
Now if GA do not believe they will need these last nine or so units for a very long time then they might just write of the "risk" you refer to.
After all it has taken the manufacturer so long to get them made/delivered/commissioned that the TOC/DfT may no longer be contractually obliged to take them on ?. I can imagine a bean counter saving money now rather than looking at the long term - and they may well be correct.
On the other hand I do think the looming demand is there - especially in the case of GA where pressure could be taken off the 745 fleet (there are not enough 745s)..
I am hoping/assuming that the reality is that the manufacturer sees its priority as getting other recently manufactured fleets (730 and 701s) out of the door. After all these last nine 720s might be the worst of the delinquents.
I would say that as far as the manufacturer goes (Bombardier back then) there seemed to be an aspiration to build the units as fast as possible. Hoping for the best teething trouble wise seems to have resulted in the need to just park up delinquent units in sidings away from Derby for rectification later as the manufacturing capacity at Derby could not be compromised. I think Bombardier took on too many orders. Now Alstom are saddled with the consequences.
Did I say 701s ? - now there is plenty of food for conjecture there !.
All I know for sure is that there seemed to be a surge of sidelined 720s in to service last November (2024) and now a lull.